Re: [PATCH v2 1/1] s390: virtio: let arch accept devices without IOMMU feature

From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Pierre Morel <pmorel@linux.ibm.com>, linux-kernel@vger.kernel.org
Cc: pasic@linux.ibm.com, frankja@linux.ibm.com, mst@redhat.com,
	jasowang@redhat.com, cohuck@redhat.com, kvm@vger.kernel.org,
	linux-s390@vger.kernel.org,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v2 1/1] s390: virtio: let arch accept devices without IOMMU feature
Date: Tue, 16 Jun 2020 08:55:18 +0200	[thread overview]
Message-ID: <74b6cf8a-d5a6-e0bf-f1c1-e453af133614@de.ibm.com> (raw)
In-Reply-To: <1592224764-1258-2-git-send-email-pmorel@linux.ibm.com>

On 15.06.20 14:39, Pierre Morel wrote:
> An architecture protecting the guest memory against unauthorized host
> access may want to enforce VIRTIO I/O device protection through the
> use of VIRTIO_F_IOMMU_PLATFORM.
> 
> Let's give a chance to the architecture to accept or not devices
> without VIRTIO_F_IOMMU_PLATFORM.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>

Shouldnt we maybe add a pr_warn if that happens to help the admins to understand what is going on?

> ---
>  arch/s390/mm/init.c     | 6 ++++++
>  drivers/virtio/virtio.c | 9 +++++++++
>  include/linux/virtio.h  | 2 ++
>  3 files changed, 17 insertions(+)
> 
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 87b2d024e75a..3f04ad09650f 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -46,6 +46,7 @@
>  #include <asm/kasan.h>
>  #include <asm/dma-mapping.h>
>  #include <asm/uv.h>
> +#include <linux/virtio.h>
>  
>  pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
>  
> @@ -162,6 +163,11 @@ bool force_dma_unencrypted(struct device *dev)
>  	return is_prot_virt_guest();
>  }
>  
> +int arch_needs_iommu_platform(struct virtio_device *dev) 
> +{
> +	return is_prot_virt_guest();
> +}
> +
>  /* protected virtualization */
>  static void pv_init(void)
>  {
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index a977e32a88f2..30091089bee8 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -167,6 +167,11 @@ void virtio_add_status(struct virtio_device *dev, unsigned int status)
>  }
>  EXPORT_SYMBOL_GPL(virtio_add_status);
>  
> +int __weak arch_needs_iommu_platform(struct virtio_device *dev)
> +{
> +	return 0;
> +}
> +
>  int virtio_finalize_features(struct virtio_device *dev)
>  {
>  	int ret = dev->config->finalize_features(dev);
> @@ -179,6 +184,10 @@ int virtio_finalize_features(struct virtio_device *dev)
>  	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
>  		return 0;
>  
> +	if (arch_needs_iommu_platform(dev) &&
> +		!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM))
> +		return -EIO;
> +
>  	virtio_add_status(dev, VIRTIO_CONFIG_S_FEATURES_OK);
>  	status = dev->config->get_status(dev);
>  	if (!(status & VIRTIO_CONFIG_S_FEATURES_OK)) {
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index a493eac08393..2c46b310c38c 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -195,4 +195,6 @@ void unregister_virtio_driver(struct virtio_driver *drv);
>  #define module_virtio_driver(__virtio_driver) \
>  	module_driver(__virtio_driver, register_virtio_driver, \
>  			unregister_virtio_driver)
> +
> +int arch_needs_iommu_platform(struct virtio_device *dev);
>  #endif /* _LINUX_VIRTIO_H */
> 